Electrical-wave filter



Aug. 21, 1923. 1,465,758

A. M. CURTIS ELECTRICAL WAVE FILTER Original Filed on; a, 1917 g7 FH'H lm/enfon- Ausfen M. Curf/IJ Patented Augizl, 1923. i 3;-

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Original Apparition m botober 0, i011, semi no. 195,311. Patent nafns ngza ama'imcn'16,.

. m1. mum and an application fled August a, 191a sum llo. 818,369.

Toall whom it my. camera:

Be it known thatvI, Aus'ran M. Commas citizen of the United States residlng at East Orange,inthe county of lfissex, State of 5 New Jersey, have invented certain new and useful Improvements in Electrical-Wave Filters, of which the following is a full, clear, concise, and exact descr ption.

This invention relates to a novel form of wave'filterandhas particular reference one which is capable of being used in radio receiving-systems for the purpose, of reducing the efl'ect. of static or atmospheric dis'-- turbances produced in the signahng system when the si als are be' receive This app ication is a ivision of A. M. Curtis applicatiomSerial Np. 195,? 71, filed October 8, 1917, fReduction of static interference in radio receiving stations, on wh1ch Patent #1,371,228 was granted on The invention is an improvement on the wave filter shown in Fig. 2 of the ap hcatron filed by E. O. Scriven, July 14, 191 Serial No. 180,589, entitled Oscillation generator.

The ,Scriven application involves the use of a wave filter for efiiciently transmitting low frequencies and suppressing hlgh frequencies, and which has been termed an ultra-filter. The present invention takes advantage of the .fact that the filter of the above-mentioned Scriven application is substantially freefrom inductance giving rise to the fact that the natural period of oscillatlon of the filter is very high'in comparison to the frequencies that are efliciently transmitted. W An object. of. the present my ention is to provide a filter of the above-mentioned type 40 with the addition of a uni-directional element such as an audion tube between adjacent filter. sections so as to prevent reaction.

between one section and another.

' ".Another object of the invention is to pro-' "vide a filter similar to the one just described but of the infra-type, that is, one suppressing relatively low' frequencies, this type also having the advant 'e of a very high natural period by reason .0 the fact that-1t 1s substantially free from inductance. I Another object of the invention is to provide a band filter, having. a very high periodof natural oscillation by reason ofthe fact thatiit is substantlally free from, inductance. This type of filter is of particular advantage. when used 1n radio receiving systems, since the energy of the static or similar-impulse on striking the filter produces only oscilla+ tions of such high frequencies that theydo not efl'ect the signal receiving instrument.

trates diagrammatically the filters shown in Figs. 1 and 2 in a simple form; and Fig. 4 1llustrates a band filter representing acornblnation of the filters shown in-Figs. 1 and 2.

Referring to Fig.1, line 1 is adapted to receive currents of varied frequencies, the low frequency components of which are to be selectively transmitted and amplified. the block F represents a filterand amplifier section, aplura ity of which may be used as represented'by the otherblocks F all of these being connected in tandem. The block' F comprises a vacuum tube 2 of the. audion type having a high resistance 3, in shunt to its input circuit, a batteryg4 which assigns a negative potential to the grid 5, and ,a

source 6 which supplies the space current for I the tube through the. high non-inductive resistance 7. The filament 8 of the, tube is grounded as shown at '9. In shunt to the output circuitof the tube 2 is. a circuit-which includes a high non-inductive'resistance 10 and a capacity 11 which grounded at 12.

The next blockF is connected in shunt to" the c0ndenser11,'as shown, and the same is true of" all succeeding filter. sections; The vacuum tube employed in each of the filter sections is essentially unidirectionally conducting so that a reaction between the filter sections is prevented. The current delivered by the last filter section E may be, amplified by an ordinary amplifier'of the audion-type, as shown in block A. In advance of the I amplifier in block A, there is provided a condenser 13 which; prevents the the output circuit of the preceding tube inthe series from assigning a potential to the amplifier A. The condenser '14 in-block F performs asimilar function. The valueof these capacities 13 and 14 is very large compared to the other reactances inthe system it) fiat their effect on the system is neg- Fig. the filter section F: is the same as'section tions of the resistance 10 and the capacity 11 have been interchanged. In Fig. 2,'the second filter section F is in shunt to the resistance 15, which together with the condenser 16 forms a shunt around the output circuit of the tube 17. In this case also a plurality of filter sections F are employed and an amplifier similar to A in Fig. 1 may be used, although this is not shown.

The operation of the filters shown in Figs, 1 and 2 may be elementarily described 1n connection with Fig. 3 in which the line 18 is adapted to receive currents of various frequencies, only some of which are'to be eficiently. transmitted. Connected to the line 18 are the resistance 19 and the capacity .20. It will be apparent that currentsof very low frequencies find a path of very high impedance through the condenser 20, so that the voltage across the condenser 20 is relativel high, the voltage across resistance 19 being relatively low, since the current is very small. If a voltage responsive device, such as a voltmeter 21 is connected across the condenser 20, it will register a' comparatively high voltage for, low frequency currents which are received by the" hne 18.- High frequency currents, however,

' find a path of low-impedance through the condenser 20, so that the voltage drop across the condenser20, as md-icated by the voltmeter 21' will be comparatively low, whereas a drop across the resistance 19 will be comparatiyely high, due to the fact that the current, is large. Of the various frequencies which are received by the line 18, the lowest frequency produces the greatest effect upon thevoltmeter 21 so that the ultimate effect is to suppress high frequency and therefore this filter is called an ultrafilter. The connection'of the voltmeter 21 across the condenser 20 is entirely analo- .gous to the connection of the second filter section F of Fig. 1 across the condenser 11. In Fig.1, however, a plurality. of such sections areemdployed, a uni-directional tube being locate between adjacent sections to prevent reaction. Furthermore, the outputiof the last filter section. is connected to an em lifiertube to bring the amplitude of these ected frequency or frequencies up to the desired value.

With regard to Fig. 3 it is apparent that low frequency currents produce a low voltage across theresistance 19, while high ein Fig. 1, except that the posi-.

accuse quencies give rise to highvoltage. If the,

next filter section, therefore, is connected across the resistance 19, the low frequencies ters shown in Fi 2.

In Fig. 4, the ters shown 111m .7 v y 2 have been combined to provide a filter for transmitting only a band of frequencies, the

infra-filter serving to suppress the lower freuencles up to a certain value and the ultralter su pressing all frequencies beyond a given va ue. In this case, the condenser 16 otential and filprevents battery 6, from assignin to the tube 17. A plurality of su'c ters may be used in tandem if desired,'each" filter having between it and the next a uni: lateral device such'as a vacuum tube, two

of which are shown in Fig. 4. The filters shown, in Figs. 1, 2 and 4 are substantially free from inductance, and they accordingly have a very tion. 7

What is claimed is: A

1. A wave filter comprising lumped r si t."-

high period of natural oscilla-r ance and comprising only one kind of lumped reactance, a source forsuppl electromotive force waves, to said filter, an 1 a unidirectional current transmitting device connected between said source and said fil tor for preventing reaction between said fil-.

ter and said source.

2. A wave filten comprising -a plurality of I filter sections, .each section com rising lumped resistance and only one kin of reactance, and oneofsaid sections com ri's-k mg means for preventing said section means comprising an amplifier device.

om i

reacting on another of said sections,.said' i 3. A wave filter comprisin a luralityof. I Q

alternate filter sections an e. ectron dis charge sections, said filter sections compris I mg lumped resistances and comprising means for rendering the natural frequency of oscillation of the sections difierent from v I the frequencies of the range to be efliciently transmitted.

4. A wave filter comprising a. plurality of filter sections each section comprising resistance andonly one kind of reactance, and a unidirectlonal current transmitting device serially connected between the sections.

. 5. A wave filter comp ng a plurality of: r26

filter sections, each section comprising a re sistance andonly capacitive reactance, and i a unidirectional" current transmitting device,

serially connected between the sections.

6. A wave filter for an electric circuit, said filter bein free from inductance and. comprising a p urality of filter sections, each-sec tioncomprisin said clrcult an said circuit.

7. A wave filter for anclecti' q circuit,said

a capacity in series with" a resistance shunted across filter being free from inductance and con 1- prising a capacity in series in said circuit and a circuit shunted across said first mentioned circuit, said shunt circuit comprising filter sections, each section hav ngv in asso-' ciation with a circuit, a series resistance and a shunt capacity followed by a series capacity and a shunt resistance, and a uni directional current transmitting device between the sections.'

11..A system for selectively transmitting high frequency working current more efficiently than relatively low frequencies, said system comprising recurring sections, each section including capacit and resistance but being substantially ree from inductance.

12. The combination of an infra filter and an ultra filter connected in tandem, each of saidfilters including capacity and resistance but being substantially free from inductance. 4

13. A transmission system comprising two vacuum tubes of the audion type and a "circuit comprising a band filter between said tubes, said band filter having lumped capacity in series in said circuit, and said filter having a natural period of os'cilla- 1 tion which is outside of the which it efliciently transmits.

14. A transmission system comprising two vacuum tubes of the audion type and a sectional wave filter between said tubes, one of said sections comprising series resistance and shunt capacity reactance and another. of said sections comprising series capacity reactance and. shunt resistance.

15. The combination of two vacuum tubes of the audion type and a connecting line therebetween, said line comprising series resistance and series condenser elements and also shunt resistance and shunt capacity cle ments, a source of energy for the first tube in the series, one of said'condensers'preventinglcu'rrent from said source from being supplied to a subsequent tube in the series.

16. A wave filter for an electric circuit, said filter comprising two circuits and only one kind of reactance, one of said two circuits comprisingresistance and being con-' nected in parallel with said first mentioned circuit, and the other of said two circuits comprising a capacity connected in series with the circuit constituted by said one circllilitl and said first mentioned circuit in para e v v v r 17. A filter comprising a plurality of sections, each section comprising lumped series impedance and lumped shunt impedance but only one kind of reactance, and each section serving to pass av range of frequencies and to substantially attenuate another range of frequencies, and a unidirectional current transmitting device serially connected between one section and the succeeding section.

In witness whereof, I hereunto subscribe my name this 6th day of August, A. D.

. AUSTEN M. CURTIS.

frequencies 

